The invention concerns a seal construction for a suction box in a suction roll in a paper machine.
Wear of seals in suction rolls has become a problem in an attempt to achieve longer servicing intervals. In a prior-art solution, in view of providing an efficient and tight suction roll, the seals are pressed by means of compressed air against the inner face of the roll mantle. In such a case, the compression force is maintained constantly, and the seal wears rapidly. In the present patent application, an efficient solution is suggested in order to avoid wear of the seal. According to the present invention, the seal rib is provided with a locking device. The seal is first pressed against the roll mantle. After generation of a vacuum in the suction box, the pressure is eliminated from the seal loading means, and the seal is locked in its holder. With the arrangement in accordance with the invention, even the water lubrication can be omitted. Further, the seals can be provided with inclined faces, which permit gradual equalization of the pressures in the perforations in the suction roll as the perforations in the roll depart from the area of vacuum along with the rotation of the roll.
The prior art related to the present invention is represented by the applicant""s earlier FI Patent Application No. 934909, in which the main principle of the invention on the whole is protected, i.e. carrying out a locking of the seal rib.
In the present new patent application, a precise, optimal solution is described for providing a locking construction. In the present invention, a locking construction is employed in which all the constructions for carrying out the locking are placed in the seal rib itself. Thus, no separate alterations have to be made in the seat.
In accordance with the present invention, as the device for locking of the seal, a separate loading device is employed, favourably a hose operating by means of air pressure. The hose has been fitted between the seal and the holder on the bottom of a groove provided in the seal. According to the invention, said hose is placed in connection with a separate piston part. At the opposite side of the seal, there is a separate rib, which is pressed against the wall of the holder. In connection with said rib, there are seal bands. The piston part and said separate rib are favourably made of reinforced plastic, such as fibreglass epoxy resin or fibreglass phenol resin or PE plastics.
The seal 10 itself consists of two component frames: a base frame 10a and a wear frame 10b. On the top of the base frame 10a, there is a separate wear frame 10b as the contact frame, which wear frame can be made of rubber graphite, carbon graphite, or plastics, such as PE, PC, PPF, PEEK, or PFTE plastic or phenol resin. The construction may further include fibre reinforcements, such as carbon fibres, glass fibres, aramide fibres, and it may also contain graphite powder. Said separate wear frame has been fixed to the base frame by gluing. The wear frame has also been attached to the base frame by means of a dovetail joint.
The seal construction in accordance with the invention for a suction box in a suction roll in a paper/board machine is characterized in what is stated in the patent claims.